When the website displays a price range like the one on the REI Co-op Merino Midweight Base Layer Long-Sleeve Crew Top for Men, item #101403, it means that some of the colors are discounted and some are full price.
In this case, the color Asphalt Brush Strip/Black is on Clearance. When you chose the size Medium, the price changed to reflect the price of the available colors in that size. The clearance priced color is not available in a size Medium. If you are an REI member you will earn 10% back on the full priced colors!
We also have some similar wool men’s base layers available for discounted prices on our Outlet.